Process for treating metal surfaces



United States Patent 3,231,425 PROCESS FOR TREATING METAL SURFACES Martin B. Sheratte, New Haven, and John A. Scott, North Haven, Conn., assignors to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Filed Apr. 24, 1963, Ser. No. 275,229 8 Claims. (Cl. 134-41) The present invention relates to an improved process for treating metal surfaces. More particularly, the present invention resides in an improved process for treating metal, especially aluminum or aluminum base alloys, so as to render the surface thereof receptive to further treatments, such as adhesive joining, painting, etc.

Mill finish metal has a surface which is unreceptive to further treatment, such as adhesive joining, painting, etc. Presently used methods for improving the receptiveness to such further treatments involve time-consuming processes which often require a plurality of steps and a complexity of materials. In addition, presently used methods frequently involve the use of expensive and hazardous chemicals, for example, the most commonly used pretreatment for adhesive joining of aluminum involves immersing the aluminum surface in a bath containing chromic and sulfuric acids at approximately 70 C. A bath of this type is quite acidic and represents a considerable hazard. In addition the treating baths heretofore employed must be frequently replenished, a procedure which is time consuming and costly. Still further, most art treatments to improve the receptivity of the surface cause etching or dulling thereof, a significant disadvantage.

Accordingly, it is an object of the present invention to provide an improved process for treating metal surfaces so as to render them more receptive to further treatments.

It is a further object to provide a process as above which expeditiously treats and cleans the metal surfaces without the necessity of a plurality of treatment steps and complexity of materials and which utilizes inexpensive and non-hazardous materials.

It is a still further object of the present invention to provide a process as above which does not result in objectionable etching or dulling of the metal surface.

Further objects and advantages of the present invention will appear hereinafter.

In accordance with the present invention it has been found that the foregoing objects and advantages may be readily accomplished and an improved method for treating metal surfaces provided which comprises contacting said surface with a dilute solution, preferably aqueous, of an acid selected from the compounds having the following formulas:

I o H-C o X H N i co.e o rr-o 0 1r cube 0 X N-I't-CO H wherein each R is lower alkyl and each X is selected from the group consisting of hydrogen, carboxyl and succinimido.

The preferred process of the present invention comprises immersing the metal surface to be treated in a 0.1 to 3 percent aqueous solution of beta-maleimidopropionic acid or beta-succinimidopropionic acid at an elevated temperature, for example, 50 to 100 C., for about 1 to 60 minutes. The metal surface is then rinsed with cool, distilled water and air-dried.

3,231,425 Patented Jan. 25, 1966 The simple and expeditious process of the present invention renders the metal surface ready for further treatment, that is, adhesive joining, painting or other surface treatments. The process of the present invention is highly successful in promoting adhesion both to structural adhesives and organic films, including vinyls, acrylics, alkyds, urethanes and epoxies. The metal surface is made surprisingly receptive to these treatments by the simple, non-hazardous and expeditious process. The present process represents a distinct advance over the cumbersome, inconvenient and often harmfulprocesses employed heretofore. Still further, the present process achieves its effectiveness despite the surprising absence of dulling or etching of the metallic surface.

The process of the present invention is readily applicable to any of the following metals or base alloys thereof: aluminum; copper; ferrous; and zinc. In addition to the foregoing metals and base alloys thereof, coated or clad products may be used, Where the coating consists of any of the foregoing metals or base alloys thereof.

, Exemplificative metals and alloys which may be employed include, but are not limited to: any of the foregoing metals in high purity; aluminum alloys 3003, 5005,

2024 Alclad, and 1100; cartridge brass; tough pitch merely representative and naturally an exhaustive list.

may be complied; however, it will be apparent to one skilled in the art that the process of the present invention is highly advantageous when employed with any of the foregoing metals or base alloys thereof.

The process of the present invention contemplates the use of a dilute solution, preferably aqueous, of the appropriate succinimido of maleimido acid or mixtures thereof. The solutions may contain from 0.05 to 10 percent by Weight of the appropriate fatty acid. Naturally the dilute aqueous solution may contain other ingredients for particular results. The aqueous solutions are naturally preferred, but other compatible liquids may be conveniently employed, such as alcohols.

The length of time of treatment will naturally vary depending upon the particular metal employed, temperature of treatment and the particular solution; generally, however, the metal should be in contact with the solution for from one minute to several days. Longer periods of time may be employed but no particular advantage is to be served by using excessive time periods. Similarly, the particular temperature will vary depending upon the foregoing factors and upon the time of treatment. The temperature should, however, be maintained in the range of 0 C. to C.

The preferred succinimido or maleimido fatty acids which may be employed are where the substituent R in the foregoing formulas is a saturated lower alkyl radical, such as succinimidoacetic acid and succinimidopropionic acid, and maleimidoacetic and maleimidopropionic acid, since these are the most readily available. Other exemplificative radicals which may be substituted for the substituent R include saturated and unsaturated aliphatic radicals, and aromatic radicals, such as phenyl and naphthyl and substituted phenyl and naphthyl, for example, chlorophenyl, nitrophenyl, etc. The substituent X may be either hydrogen, carboxyl or succinimido.

The succinimido and maleimido compounds used in the present invention may be prepared by admixing stoichiometric quantities of succinic or maleic anhydride and the appropriate amino acid (one mole succinic or maleic anhydride per amino group). The mixture is heated to a preferred temperature of between to C. and maintained at that temperature for preferably from 30 minutes to 4 hours until water ceases to be evolved.

The resultant product is crystallized from any appropriate solvent.

The present invention encompasses the treatment of the metal surface with the appropriate dilute solution and is not limited to immersing the metal in the solution. In other words, numerous alternatives may readily suggest themselves to one skilled in the art, such as spraying or brushing the metal surface with the dilute solution.

The present invention will be more readily apparent from a consideration of the following illustrative examples.

Example 1 6" x 4" panels of Alclad 2024 T3 aluminum were immersed in a 0.1 percent solution of succinimido acetic acid at 95 C. for five minutes. They were then rinsed for a few moments in cool distilled water and air dried. They were subsequently bonded in pairs using an epoxy adhesive. The bonded panels were cut into 1" test coupons, some of which were tested in the as-made condition, and some after 48 hours immersion in boiling water. For comparison, similar test coupons were prepared from panels which had been degreased only before bonding. The results are as follows:

As-Made Strength After Strength, 48 Hours in p.s.i. Boiling Water,

p.s.i.

Treated coupons 2, 1, 740 Degreased only coupons 1, 780 0 Example 2 A set of panels as in Example 1 was treated in a manner after Example 1 with the exception that succinimido propionic acid was used instead of succinimido acetic acid. The results are as follows.

As-Made Strength After Strength, 48 Hours in p.s.i. Boiling Water,

p.s.i.

Treated coupons 2, 720 2, 390 Degreascd only coupons 1, 710 0 Example 3 A set of panels as in Example 1 was treated with succinimido propionic acid in the same manner as in Example 1. For comparison, similar test coupons were prepared from panels which had been subjected to the conventional chromic acid etch pretreatment for adhesive bondin The conventional pretreatment comprised immersion for ten minutes in a solution containing 30 parts by weight water, 1 to parts by weight sulfuric acid (s.g. 1.84), and 1 part by weight sodium dichromate at 70 C. The results are as follows:

As-Made Strength After Strength, 48 Hours in p.s.i. Boiling Water,

p.s.i.

Panels treated with succinimido propionic acid 2, 310 1, 720 Panels treated with conventional etch 3, 080 1, 230 Panels degreased only 1, 790 0 Example 4 Example 3 was repeated using cartridge brass instead of aluminum. For comparison similar test coupons were prepared using a conventional chromic acid pretreatment. The conventional pretreatment comprised 255 grams water, grams sodium dichromate, and 30 grams sulfuric acid for 2 to 3 minutes at room temperature. The results are as follows:

As-Made Strength After Strength, 2 Weeks in p.s.i. Boiling Water,

p.s.i.

Panels treated with succinimido propi' onic acid 1, 080 150 Panels treated with conventional etch--- 1, 150 47 5 Example 5 Example 4 was repeated using cold rolled steel instead of aluminum. For comparison test coupons were prepared pretreated with 50 percent hydrochloric acid for 5 minutes at room temperature. The results are as follows:

As-Made Strength After Strength, 2 Weeks in p.s.i. Boiling Water,

p.s.i.

Panels treated with succinimido propionic acid. 2, 040 1, 090 Panels treated with hydrochloric acid... 2, 715

Example 6 In a manner after Example 3 electrolytic tough pitch copper was bonded after pretreatment with succinimido propionic acid. Good results were obtained.

Example 7 In a manner after Example 1 Alclad 2024 T3 aluminum was bonded after pretreatment with maleirnido propionic acid. Good results were obtained.

Example 8 Example 3 was repeated except that succinimidoglutarnic acid was used and after pretreatment the panel was rinsed in hot water. The succinimidoglutamic acid has the following formula:

Example 9 In a manner after Example 1 Alclad 2024 T3 aluminum was bonded after pretreatment with disuccinimido lysine. Dlsuccinlmido lysine has the following formula:

CHE-CO N-CHC02H C O-CHz CHr-CO COCH2 Good results were obtained.

This invention may be embodied, in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in-all respects illustratlve and not restrictive, the scope of the invention being 1nd1cated by the appended claims, and all changes'which come within the meaning and range of equivalency are intended to be embraced therein.

What is claimed is:

1. A process for treating a metal selected from the group consisting of the following metals and base alloys thereof: aluminum, ferrous, copper and zinc, which comprises contacting said metal for at least one minute at a temperature from 0 to 100 C. with a dilute solution consisting essentially of an acid selected from the compounds having the following formulas:

wherein each R is lower alkyl, each X is selected from the group consisting of hydrogen, carboxyl and succinimido, and wherein said acid is present in a concentration of from 0.5 to 10 percent.

2. A process according to claim 1 wherein said temperatur'e is from 50 to 100 C. and said concentration is from 0.1 to 3.0 percent.

3. A process according to claim 1 wherein said acid is succinimidoacetic acid.

4. A process according to claim 1 wherein said acid is succinimidopropionic acid.

5. A process according to claim 1 wherein said acid is succinimirloglutamic acid.

6. A process according to claim 1 wherein said metal is an aluminum base alloy.

7. A process according to claim 1 wherein said metal is a ferrous alloy.

8. A process according to claim 1 wherein said metal is a copper base alloy.

References Cited by the Examiner UNITED STATES PATENTS 2,318,559 5/ 1943 Percival l488 2,692,187 10/1954 Chester et -al 252-79.4 2,872,301 2/1959 Mas-sengale et al.

ALEXANDER WYMAN, Primary Examiner.

JACOB STEINBERG, Examiner. 

1. A PROCESS FOR TREATING A METAL SELECTED FROM THE GROUP CONSISTING OF THE FOLLOWING METALS AND BASE ALLOYS THEREOF: ALUMINUM, FERROUS, COPPER AND ZINC, WHICH COMPRISES CONTACTING SAID METAL FOR AT LEAST ONE MINUTE AT A TEMPERATURE FROM 0 TO 100*C. WITH A DILUTE SOLUTION CONSISTING ESSENTIALLY OF AN ACID SELECTED FROM THE COMPOUNDS HAVING THE FORMULAS: 